Valve stem



FIG. 1 is a front perspective view of a valve stem showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3. is a left side elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a back side elevation view thereof; and,

FIG. 6 is a top view thereof. 

The ornamental design for a valve stem, as shown. 